1. Field of the Invention
The invention is directed to a vehicle wheel.
2. Discussion of the Prior Art
When a vehicle wheel, comprising a rim and a wheel disk center and convex wheel disk which are connected therewith, is mounted on a vehicle, the wheel disk center or convex wheel disk is connected in a frictional engagement with the hub or brake drum by wheel bolts. The wheel bolts are tightened by a torque wrench in order to generate a defined, sufficiently large longitudinal force along the bolt. The magnitude of the required bolt longitudinal force is determined, among others factors, by the quantity of bolts, the friction diameter of the contact surfaces, the friction coefficients between the connection elements, and the driving torque or braking torque to be transmitted. An added safety factor is imposed on the required bolt longitudinal force which takes into account the forces acting on the bolt when the wheels are rolling.
The connection boss and countersink of the wheel are clamped with the hub or brake drum via the longitudinal force of the bolt. The countersink has the function of opposing an elastic resilience to the bolt longitudinal force to the extent of elevated values such as occur as a result of misuse, e.g., oiled bolts or excessive tightening torques, since a plastic flow would lead to a decrease in the bolt longitudinal force and accordingly ultimately to a loosening of the wheel bolts.
Known constructions of connection bosses derive their spring rigidity in the direction of the longitudinal axis of the bolt from a bending of the material arranged annularly around the countersink. Constructional stiffening is known for the purpose of increasing spring rigidity over that of normal plate thickness. One possibility consists in an inward reverse drawing or camber of the region of the connection boss located inside radially. Moreover, this shape has the advantage of an outward enlargement of the contact surface relative to the wheel bolts compared with a simple camber. For example, reference is had to the wheel catalog of Mannesmann Kronprinz AG, 1990/1991 Issue, bottom of page 28. A disadvantage in prior constructions of the connection boss is the clear dependency of the stiffness of the connection boss on the plate thickness and on the material strength of the starting material.
A wheel comprising a profiled rim and a convex wheel disk connected therewith in the drop base region by means of welding is known from U.S. Pat. No. 3,664,708. To prevent cracking in the connection boss as the result of excessive tightening of the wheel bolts, it is suggested to arrange a flange-like bushing in the connection boss. The region of the bushing constructed in the manner of a flange lies on the side facing the hub or brake drum and must be inserted through the connection boss before the wheel is mounted. After placement on the wheel, a cone of the front region of the bushing is formed by of tightening the wheel nut. This cone comes to rest on the edge region of the connection boss, but only when the end face of the flange-like region of the bushing rests on the hub or brake drum. A disadvantage in this design is that special bushings must be produced which can easily fall out of the connection boss during the mounting of the wheel until the cone fixing the bushing is formed. Further, this arrangement is suitable only for wheels with stud pins arranged at the hub or brake drum, since the bushings can fall out easily during mounting in the otherwise conventional wheel bolt fastening. Another disadvantage consists in that the bushing always fits only one type of wheel, so that for a hundred different wheel types, a hundred different bushings will have to be produced and stocked. Further, confusion can lead to the wrong bushing being used. Another disadvantage is that at least two setting gaps remain as a result of the two-part arrangement. This is very prejudicial to the stability of the bolt longitudinal force. Moreover, the bending spring is already highly loaded in the course of mounting, since the cone of the bushing is formed by means of the wheel nut.
French reference FR-A-25 39 079 discloses a special wheel hub construction. The sole figure shows a section of the vehicle wheel, including a region of the convex wheel disk. The convex wheel disk is provided with a plurality of connection bosses for the wheel bolt holes arranged along the circumference of the bolt pitch circle. The connection boss has a conical countersink, and the region surrounding the countersink is cambered outward. The region of the connection boss surrounding the countersink is significantly thicker and all cross-sectional planes than the more remote region of the convex wheel disk. The region directly adjoining the countersink has the greatest thickness which then decreases in a continuous manner radially outward as viewed from the axis of the countersink and then merges in a rounded manner into the adjoining region. This adjoining region has a virtually constant thickness which corresponds substantially to the initial thickness of the round blank for the integral forming of the convex wheel disk.